yAxisIndex: 1, symbolSize: 10,

These are two separate properties of a series in a chart.

- `yAxisIndex` specifies which y-axis the series should be plotted against. If there are multiple y-axes in the chart, each with a different scale, this property allows you to choose which one to use for a particular series. The value is an integer, representing the zero-based index of the axis. For example, if there are two y-axes in the chart and you want the series to use the second one, you would set `yAxisIndex: 1`.

- `symbolSize` specifies the size of the symbols used to represent data points in the series. The value can be a fixed number, or an array of numbers (one for each data point) to allow for varying sizes. In this case, the value is set to 10, which means each symbol will be 10 pixels in diameter (assuming the chart has not been scaled or zoomed).

Note that these properties apply to a series, which is a collection of data points that are represented together on the chart (e.g. a line chart with multiple lines or a scatter plot with multiple sets of points). Each series can have its own yAxisIndex and symbolSize settings.